The present invention relates to diodes in semiconductor devices that function as fuses or anti-fuses and, more particularly, to such diodes having an electrical conductivity that is alterable by external application of energy.
Fuse and anti-fuse structures are used widely in semiconductor devices for logic programming, repair of defective circuits, and other purposes. Anti-fuses have an increased electrical conductivity when activated and fuses have a decreased conductivity when activated. Known fuses and anti-fuses are activated by application of laser energy, which causes a metal element to melt and/or vaporize, thereby creating an open circuit in the case of a fuse and a short circuit in the case of an anti-fuse.
Recently, copper has replaced aluminum as a wiring material for certain wiring levels in semiconductor devices. Many advanced dielectric materials used between copper wiring levels may have a porous structure with a low dielectric constant, k value, i.e., a k value of about 2. These dielectric materials cannot withstand application of laser energy at known intensities and for known periods of time used to activate a fuse or anti-fuse in an adjacent wiring level. As a result, conventional fuses and anti-fuses are not adapted for use when adjacent or underlying porous dielectric materials have a low k value.
Copper oxidation problems in semiconductor devices having copper wiring also limit the use of conventional fuses and anti-fuses of the type that are xe2x80x9cblownxe2x80x9d by laser energy. Unlike aluminum, copper does not self passivate. When a portion of a copper wiring line in silicon dioxide is laser deleted, a crater is created in the area where the portion of the line is deleted. This exposes the ends of the copper wiring line proximate the crater, which can result in oxidation of the line ends. Steps must be taken to prevent such oxidation from affecting other circuits in the semiconductor device, which often adds to the cost and complexity of the semiconductor fabrication process. In addition, because more energy is required to xe2x80x9cblowxe2x80x9d a copper fuse than an aluminum fuse, there is an increased risk of heating the substrate adjacent the fuse to the point where cracks are formed in the oxide over the substrate. When these cracks intersect copper wires, oxidation of the wires can result. Eventually, such oxidation can result in a break occurring in the copper wire, resulting in a reliability fail.
One aspect of the invention is a diode in a semiconductor device that is made in accordance with a process beginning with the step of providing a diode having a p region and an n region. The regions are positioned to form a pn junction with a first electrical conductivity. Next, energy is applied to the diode from a source external to the semiconductor device at an intensity and for a period of time sufficient to cause the electrical conductivity to change to a second electrical conductivity differing by at least 10% from the first electrical conductivity.
A second aspect of the present invention is a method of altering the electrical conductivity of a diode in a semiconductor device. The method comprises the steps of providing a diode having a p region and an n region. The regions are positioned to form a pn junction with a first electrical conductivity. Then, energy is applied to the diode from a source external to the semiconductor device at an intensity and for a period of time sufficient to cause the first electrical conductivity to change to a second electrical conductivity differing by at least 10% from the first electrical conductivity.
These and other aspects of the present invention are described in more detail below and are further defined in the appended claims.